Add a mojo::test::ScopedTestDir and convert tests to use it.

mojo/edk/test/scoped_test_dir.cc

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "mojo/edk/test/scoped_test_dir.h"
+
+#include "base/files/file_path.h"
+#include "base/files/file_util.h"
+#include "base/logging.h"
+
+namespace mojo {
+namespace test {
+
+ScopedTestDir::ScopedTestDir() {
+  CHECK(temp_dir_.CreateUniqueTempDir());
+}
+
+ScopedTestDir::~ScopedTestDir() {}
+
+util::ScopedFILE ScopedTestDir::CreateFile() {
+  base::FilePath unused;
+  return util::ScopedFILE(
+      base::CreateAndOpenTemporaryFileInDir(temp_dir_.path(), &unused));
+}
+
+}  // namespace test
+}  // namespace mojo